The field of invention relates to direct access data storage, generally. More specifically, the invention relates to the improved thermal stability of GMR based SV sensors for use within magnetic heads.
Hardware systems often include memory storage devices having media on which data can be written to and read from. A direct access storage device (DASD or disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form. Magnetic heads, when writing data, record concentric, radially spaced information tracks on the rotating disks. Magnetic heads also typically include read sensors that read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, the defining structure of MR heads, can read stored data at higher linear densities than thin film heads. A MR head detects the magnetic field(s) through the change in resistance of its MR sensor. The resistance of the MR sensor changes as a function of the direction of the magnetic flux that emanates from the rotating disk.
One type of MR sensor, referred to as a giant magnetoresistive (GMR) effect sensor, takes advantage of the GMR effect. In GMR sensors, the resistance of the MR sensor varies with direction of flux from the rotating disk and as a function of the spin dependent transmission of conducting electrons between magnetic layers separated by a non-magnetic layer (commonly referred to as a spacer) and the accompanying spin dependent scattering within the magnetic layers that takes place at the interface of the magnetic and non-magnetic layers.
GMR sensors using only two layers of magnetic material separated by a layer of GMR promoting non-magnetic material are generally referred to as spin valve (SV) sensors. In an SV sensor, one of the magnetic layers, referred to as the pinned layer, has its magnetization xe2x80x9cpinnedxe2x80x9d by exchange coupling with an antiferromagnetic layer. Due to the relatively high internal anisotropy field associated with the pinned layer, the magnetization direction of the pinned layer typically does not rotate from the flux lines that emanate from the rotating disk. The magnetization direction of another magnetic layer (commonly referred to as a free layer), however, is free to rotate with respect to the flux lines that emanate from the rotating disk.
FIG. 1 shows a prior art SV sensor structure 100 comprising a seed oxide layer 102 formed upon a substrate layer 101. The seed oxide layer 102 helps properly form the microstructure of free magnetic layer 103. Note that free magnetic layer 103 may be a multilayer structure having two or more magnetic layers (e.g., layers 103a, 103b). The non-magnetic spacer 104 and pinned 105 layers are formed atop free magnetic layer 103. Finally, the antiferromagnetic (AFM) layer 106, used to pin the magnetization direction of the pinned layer 105, is formed atop the pinned layer 105.
A problem with structures such as or similar to that shown in FIG. 1 is the degradation of the magnetoresistive effect after one or more high temperature anneals (which are typically performed in manufacturing environments). FIG. 2 shows the degradation of MR effect, as a function of annealing temperature, that has been observed for a particular SV sensor structure similar to that of FIG. 1. A structure exhibiting improved MR effect degradation, along with other possible advantages, is desirable.
An apparatus comprising an oxide layer, a magnetic barrier layer over the oxide layer and a magnetic layer over the magnetic barrier layer. The magnetic barrier layer has a thickness that prevents reaction between the magnetic layer and the oxide layer.